1. Field of the Invention
The present invention relates to a shock absorber, and in particular, to a shock absorber of a built-in damper type provided with an oil lock structure, which can achieve a desired oil lock effect and prevent flaws of an oil seal caused by a high pressure function.
2. The Related Art of the Invention
For example, Japanese Unexamined Patent Publication No. 6-173999 has disclosed the technology with respect to a conventional shock absorber of a built-in damper type provided with an oil lock structure.
The conventional shock absorber is provided with an outer tube, and an inner tube located inside the outer tube and fixed to a lower end member of the shock absorber where the outer tube and the inner tube are arranged to slide with each other and a damper is disclosed inside them. The damper slides while the inner tube slides on an inner surface of the outer tube, to produce a damping force. When the shock absorber is at the maximum compression state, an oil lock piece provided in a cylinder of the damper enters into an oil lock case located in an end of the inner tube. The entering of the oil lock piece into the oil lock case causes the volume inside oil lock case to reduce, increasing the pressure therein. Based upon this pressure increase, a predetermined oil lock effect is achieved.
Meanwhile, an oil chamber is provided between the oil lock piece and a rod guide in this technology. A highly pressurized operating oil at the oil lock state does not act on the oil chamber due to the action of the oil lock piece. Accordingly the high pressure does not exert on an oil seal provided in the lock guide. Further, a communicating bore communicating between the oil chamber and an outside thereof is provided in the cylinder. In case the highly pressurized operating oil enters into the oil chamber caused by wear of the oil lock piece or the like, the communicating bore is arranged to discharge the highly pressurized operating oil from the oil chamber to the outside thereof, protecting the rod guide provided with the oil seal from the highly pressurized operating oil.
According to the conventional technology, when the highly pressurized operating oil enters into the oil chamber, the highly pressurized operating oil is released to the outside thereof, thereby protecting the oil seal. The oil lock piece, however, allows a predetermined clearance for securing slide performance of the piston rod.
Namely, according to the conventional oil lock structure, flow of the highly pressurized operating oil passing through the clearance provided in the oil lock piece portion is designed to be allowed. An oil lock effect, however, is achieved by enclosing an operating oil inside the oil lock chamber defined between the oil lock piece and the oil lock case. Therefore, since in the conventional oil lock structure, a leakage of the highly pressurized operating oil from the oil lock chamber is allowed, the conventional oil lock structure results in that a predetermined oil lock effect can not be achieved.
In view of the above, there exists a need for a shock absorber which overcomes the above-mentioned problems in the related art. The present invention addresses this need in the related art and also other needs, which will become apparent to those skilled in the art from this disclosure.